Fluid pressure relay



Feb. 19, 1952 E.- W. FITCH 2,586,637

FLUID PRESSURE RELAY Original Filed July 14, 1941 FIG. l 8B /TWQM' 'yPatented Feb. 19, 1952 FLUID PRESSURE RELAY Edward W. Fitch, Poland,Ohio, assignor to Bailey Meter Company, a corporation of DelawareOriginal application July 14, 194:1,` Serial No. 402,386. Divided andthis application April 13, 1948, Serial No. 20,796

4 Claims. 1

This invention relates to control systems for maintaining a conditionsuch as pressure, temperature, level, electromotive force, or the likeatfor substantially at a desired value through regulating the rate ofapplication of an agent producing, maintaining or otherwise affectingthe condition.

In accordance with my invention the rate of application of the agent isvaried in accordance with the second derivative of the magnitude of thecondition with respect to time, or in other words in accordance with therate of change of the rate of change in the magnitude of the condition.In order for control systems establishing a control eiTect varying inproportion to the magnitude of a condition with respect to time, or inaccordance with the rst derivative thereof to act, it is necessary thatthere be an appreciable change in the magnitude of the condition beforethe control effect will have changed Sulliciently to produce a materialeffect on the rate of application of the agent. A consideration of theprinciples of my invention will indicate, however, that the controleiect produced thereby changes most rapidly at the instant the conditionis changing most rapidly, and accordingly acts to correct the rate ofapplication of the agent before a material change in the magnitude ofthe condition has occurred. In other words, changes in the magnitude ofthe condition are anticipated, and proper correction in the rate ofapplication of the agent made before such change has produced anappreciable departure in the magnitude of the condition from thatdesired. In order that the condition will be restored eX- actly to thedesired magnitude after departure thereform my invention furthercontemplates modifying the control of the agentin accordance with thesecond derivative of the magnitude of the condition by controlresponsive to the rst derivative of the magnitude of thecondition, whichmay in turn be modified by a control in response to the magnitude of thecondition with respect to time. .Y

I will describe my invention as applied to control systems wherein thecontrol effect established by the condition responsive device is avariable uid pressure.

In the drawings:

Fig. 1 is a diagrammatic illustration of an embodiment of my invention.

Fig. 2 is an elevation view in cross section of a preferred form ofpilot valve.

Fig. 3 illustrates a modification of a part of the control system showninFig. 1.

Referring to Fig. 1, I 4therein show an energy utilizing device, such asa tank I, which is maintained at a predetermined or desired temperatureby an agent such as steam, for example, supplied through a conduit 2, inwhich is located a regulating valve 3. The temperature Within the tank Iis determined by means of a thermometric system comprising a bulb 4connected to a Bourdon tube 5 by means of a capillary 6. The bulb 4,Bourdon tube 5, and capillary 6 are charged with an inert gas, liquid,or vapor, so that the pressure therein varies in consonance withvariations in temperature within the tank I. As the temperature Withinthe tank I increases the free end of the Bourdon tube 5 is positioned ina counterclockwise direction, and as the temperature decreases in aclockwise direction. Through the agency of devices hereinafter to bedescribed the valve 3 is positioned by a iiuid pressure established bythe Bourdon tube 5 to vary the rate of flow of steam to maintain thetemperature within the tank I at the desired value. The thermometricsystem comprising thebulb 4, capillary 6 and Bourdon tube 5 has beenillustrated merely by Way of example, it being evident that any suitablecondition responsive device, such as a resistance thermometer,potentiometer pyrometer, rate of iiow meter, etc. may be substituted,depending upon the particular condition and value of the condition to becontrolled.

Positioned by the free end of the Bourdon tube 5 is a movable valve stem1 of a pilot valve 8 illustrated as being of the type forming thesubject matter of United States patent to Clarence Johnson datedSeptember 15, 1936, No. 2,054,464. The pilot valve 8 is shown in crosssection and to larger size in Fig. 2. A fluid under pressure, such ascompressed air, is admitted to the pilot valve I3 through an inlet `port9, which is connected to a passageway Ill running longitudinally throughthe body of the pilot valve and open at either end to the atmosphere. Aow of pressure fluid is maintained from the inlet port 3 throughthepassageway I0 and exhausted to the atmosphere.

The movable valve member 'I carries lands II and I2 which are ofslightly less diameter than the passageway I0, so that a pressuregradient is established by the pressure uid in flowing past them.Immediately adjacent the land II is an outlet port I3, and adjacent theland I2 is a similar outlet port I4. The positions of the lands I I andI2 relative to the outlet ports I3 and I4 determine the pressureestablished thereat. As

the movable valve member 'l is moved upwardly,

passes by means of a flexible bellows 46. By virtue of this arrangementthe only force acting upon the member 44 and tending to cause it to movein one direction or the other from the neutral position is the netdifference in forces created by the difference in pressures within thechambers 33, 34 and 36, 31. Thus assuming that the member 44 is in theneutral position, if a change in pressure occurs Within the chamber 33,then the member 44 will be moved upwardly or downwardly, causing thepressure within the chamber 31 to change, and causing a correspondingmovement of the control valve 3. Likewise a change of pressure withinthe chamber 34, 36 or 31 will cause a movement of the member 44. If byVirtue of changes in pressure in other chambers of the relay the forcesacting upon the member 44 are again neutralized, the latter will berestored to the neutral position and the pressure within the chamber 31thereafter remain constant until there is a further unbalance of forces.

The chamber 31 is shown as being connected to the chamber 36 through apipe 48 in which is disposed an adjustable bleed valve 49. Likewise thechamber 36 is shown as being connected to the chamber 34 through a pipe90 in which is disposed an adjustable bleed valve 5I. For purposeshereinafter more fully discussed the chamber 34 is also connected to avolume chamber diagramm-atically illustrated at 52.

The bleed valves 49 and 5I are adjustable so that any relative rates ofbleed may be obtained between the various chambers. Usually I preferthat the bleed valve 49 be adjusted for a relatively fast bleed, whereasthe valve 5l be adjusted for a relatively slow bleed. Assume, however,for purposes of illustration and as an aid in understanding theinvention, that the bleed valves 49 and 5l are adjusted to permitunrestricted flow between the chambers 31, 36 and 34. Under suchconditions the pressure within the chamber 34 will alway counteract orbalance that within the chamber 36, so that no force will be producedacting either to position the member 44 upwardly or downwardly.Therefore the pres- I sure within the chamber 33, in order for themember 44 to be in the neutral position, must be balanced by thatexisting within the chamber 31. ment of bleed valves 49 and 5! the relay32 will operate to vary the pressure within the chamber 31 s0 that themember 44 is substantially instantaneously restored to the neutralposition after departure therefrom and also that the pressure withinchamber 31 is maintained equal .to that in chamber 33. For example, uponan increase in pressure within the chamber 33, causing the member 44 Atomove downwardly, the inlet valve 39 will open, thereby permitting thepressure within the chamber 31 to increase. Such increase in pressure,producing a force acting upon the member 44 in the opposite direction tothe force produced by the pressure within the chamber 33, will restorethe member 44 to the neutral position when the increase in pressurewithin the chamber 31 is equal to the increase in pressure within thechamber 33, the pressures within chambers 36 and 34 counter-balancingeach other and having no effect on the operation of the relay.

While in actual operation the bleed valves 49 and 5I are never adjustedso that pressures within chambers 31, 36, and 34 are instantaneouslyequalized, such a condition has been discussed It will be observed thatwith this adjustfor the reason that ultimately it is the cc'utldition"1which will existregardless of the adjustment of the bleed valves 49andf5l. That is so say, regardless of the yadjustment of the bleedvalves 49 and 5l, and regardless of the temporary effect which may besecured by such adjustment, ultimately whatever eiect the relay 32 mayhave on the loading pressure transmitted to the servomotor 43 isremoved, so that only that produced by the relay l1 remains. Thus, asnow Vwill be explained, the relay 32 acts merely to produce a temporaryeffect upon the loading pressure in a direction and amount to materiallyincrease the speed with which the temperature within the tank I isrestored to the desired value after de-' parture therefrom, and also theexactness with which the temperature within the tank l is maintained 4atthe desired value.

Assume now that the bleed valve 49 is left sub.-

stantially open, Whereas the bleed valve 5| is..

practically closed so that only a slow seepage of pressure fluid occursfrom the chamber 36 to the chamber 34. Under this adjustment upon achange in pressure within chamber 33, the member 44 will be displacedfrom the neutral position, thereby opening the supply valve 39 or theexhaust valve 40. As pressures within chambers 31 and 36 will equalizesubstantially instantaneously. it is evident that the pressure withinthe chamber 31 will either go to a maximum or to a minimum. Thispressure being transmitted to the diaphragm servo-motor 43l willlikewise cause the valve 3 to move to a sub,- stantially open or closedposition. Thereafter as pressure fluid gradually seeps between thechambers 34 and 36, the pressure within cham-- ber 36 will be graduallycounterbalanced, so that when the pressure within the chamber 34 isequal to that within chamber 36 the change in pressure within chamber 31will be equal to the original change occurring in chamber 33. Thusultimately the entire eiiect of the relay 32 will be removed, so thatmerely the change in pressure produced by the relay I1 will be eiectiveupon the diaphragm motor 43.

Usually it is preferable, upon a change in loading pressure occurringwithin the chamber, 33, that the pressure within the chamber 31 doesVnot go to a minimum or maximum, but that it changes an amountproportional to the change in pressure within the chamber 33, althoughof greatly amplified amount. This-I accomplish 1 by adjusting the bleedvalve 49 so that the. pres` son that as the pressure within chamber 36.changes it will cause a further change in pres-: sure within the chamber31, which latter changer. will cause a further change inpressure.within` the chamber 36, which operation will continue` until a minimumor maximum pressure is reached,

or the eiectiveness of the pressure within the chamber 36 is partiallyor wholly counterbalanced by the pressure Within chamber 34. This latteraction is obtained by the seepage of pressure uid between chambers 34and 39, s'othat' as hereinbefore explained when' the pressure withinchamber 34 is equal to that within chamber 36 the change in pressurewithin chamberS 31 will equal that within the chamber 33.

`It is evident that by proper adjustment of asados??tl'iefbleed.valves!!!l and 51 any desiredterripcnaryv changef inf.pressure within the: chamber31 maybeebtained forafgiven changeinpressurewithfin: thes chamber 33,' and that,likewise.` such. temporarychange: may be maintainedv for any desited. increment 'of time. Theparticular adjustmentsxof theA bleedvalves 49 'andY 5lv producingV bestvresults must'of course be determined by inv Fig.. 1i connects the;chamber 36vv with` the chamber 31,-. whereas the. pipe 592 connectsVthe,

chambers and 34. The operation of the relay show-n. inFig. 3"-is thesameY as that 4shown intFig-..1. The modif-led arrangement foithetpipes. l/ands!) in some instances facilitating theease. withwhichth'e relay may be adjustedto obtain optimum results. '-Ihusrv it isevident that in theY arrangein'entr shown in Fig. 1 the: rate atvwhichifpressure #fluid will seep fbetweenchambers' fand 36 isnecessarily ydependent upon therate atwhichpressure -luid seeps betweenthe; chambers 36 and' A3l.. In the. arrangement shown in Fig. 3 the'seep'ageof pressurenuidbetweenz cham*- bers Bland 31 is independent oftheseepage: of pressure fluid between chambers 36 and 31. In general,however, I have found that either ar rangement iis satisfactory, for thevalve 5| is usual-liyfadjustedfor a much slower rate ofh bleed than-isthe valveL 49, and 'accordingly the arrangement of. the relay -3'2`shown in Fig. 1 will. give substantially lsame'` type "of operationasthe relay shown in Fi'g..-3.\

In. operation,I assuming an` increase in tem"- perature within`the-tanki'l th'epilct valvea' will act to produce aehangef inloading.pressure: lof proportionate; amount.` The relay I1 will. operatevtoestablish in. the vchamber 22.4 ak change in pressure corresponding:to the change in, loading pressure established .by the. .pilot 8,. andthere'- aftenaslow continuing change so. long as the temperature withinthetank l remains-at, a value other than. that desired. The pressureestab"-A lished in the; chamber 22;,is transmitted to chamber33fof relay32.. The change: in' pressure: withiin. chamber: 33' causes; animmediate change. in pressure within `the chamber 31 andzby virtue oftheaiding action of the relatively fast bleed between the chamber 31 andchamber 36.v the practical' effect 'of the relay-321 is to: produceI achange inA pressure withinV the chamber 3.1 of much greater magnitudevthanA the-:change in pressure within' the chamber 33. The: changei inpressure 'within chamber -31` willllikewi-secontinue. to increasedueftothe regenerative elect ofV the pressure within the chamber. 35.Gradually pres sure flu-id will/seepthrough` bleedl valve" 5i from thechamber 35 to thechamber S4. The increase in. pressure withinv chamber34 will neutralizetheeiectof the pressure within the chamber 36', sothat gradually the pressure 'within' the chamber 31 will be restoredtowardlits original value; and. ultimately the change in pressurerwithinchanrf ber 31 (and line 4I) will be the sameV as that which occurred inthe chamber 33i In other wordt.` the pressure within chamber 34 may besaidto; degenerate theffeggenerativeiy amassed change inpressureinitiallyfoccurring witlfiin` the.

chamber 31 until the uid Vprcssurecontrol effect in line 4l isrestoredto its unamplied changed value. I

Changesiin-,pressure within the chamber'i are transmittedto thediaphragm vservo-motor '43 of the Lvalveft. It will be noted that in theexample just/described, immediately upon the'increase in tempera-tureAwithin the tank l, the valve-3 will be positioned in a closingdirection a relatively large amount,and then-gradually will be movedtoward an open position, but will notV be restored to the position it'originally had, due to. the action ofthe relayl l1. `It will further benoted that the amount of theV original movement ofV the valve 3 in aclosing direction will depend in part upon the rapidity with which thetempera-ture within the tank I isi changing. That is to say, the morerapid is the increase in' temperature the greater will Ibefthe movementof the valve 3 in a closing direction. Thus notwithstanding that thetemperature within the tankV l has not changed a material amount fromthe desired value. if the temperature is actually changing at a rapidrate the-valve -3 will be positioned a relatively larger amount in aclosing direction temporarily and then gradually as the temperatureceases to change the valve -3 will be positioned in an opening directionan amount depending upon the amount which the temperature has departed`from the desired value.

While I have illustrated and described a preferred embodiment or'myYinvention, it will be apparent that various `changes andfmodications maybe made without departing from its spirit and scope.

This application is a division of my copending parent application SerialNo. 402,386 led J uly 14, 1941, now Patent 2,441,405.

What I. claim as new, and desired to secure by LettersPatent oftheUnited States, is:

1. -A pneumatic relay. including, a iirst and second chamber separatedby a press-ure sensitive wall and a third and fourth chamber separatedby a second .pressure sensitiveV wall, a movable member connecting 'saidpressure sensitive walls, supply and exhaust valve means in saidfourthchamber operated by said movable member, a rst restricted pressuretransmitting connection between the. second and `fourth chambers, and a.

second restricted pressure transmitting connection between the thirdandv fourth chambers.

'2. Ajpneumatic pressure relay. including, a first andY second chamberseparated by a pressure sensitive wall and. a third and fourth chamberseparated by a second pressure sensitive wall, a movable memberconnecting said pressure sensitive walls, supply and exhaust valve meansin said fourth chamber operated by said movable member, a first pressuretransmitting connection between the second and fourth chambers, a sec-Yond pressure transmitting connection between thethird and fourthchambers,A and means ree stricting at least one of the pressuretransmitting connections.

3. A pneumatic relay including, a first and second chamber separated bya pressure sensitive wall and a third and fourth chamber separated by asecond pressure sensitive wall, a movable member connecting saidpressure sensitive Walls, supply and exhaust valve means in said fourthchamber operated by said movable member, aA first pressure transmitting.connection between the second andfourth chambers, a second pres;-

9 sure transmitting connection between the third and fourth chambers,and an adjustable restriction in at least one of the pressuretransmitting connections.

4. A pneumatic relay including, a rst and second chamber separated by apressure sensitive Wall and a third and fourth chamber separated by asecond pressure sensitive Wall, a movable member connecting saidpressure sensitive walls,

supply and exhaust valve means in said fourth 10 Number 1i) connectionbetween the third and fourth chambers with an adjustable restriction.

EDWARD W. FITCH.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Name Date 2,098,914 Gorrie Nov. 9, 1937 2,117,800Harrison May 1'7, 1938 2,360,889 Philbrick Oct. 24, 1944 2,476,104 MasonJuly 12, 1949

